Secure Digital (SD card) interface
Zephyr can communicate with an attached SD card either using a system’s native SD card interface or over SPI (Serial Peripheral Interface). Some devices can also communicate with MMC (MultiMediaCard) devices.
Applications can use Zephyr’s the disk access API to use SD cards as storage devices, or Zephyr’s SD card subsystem to directly read from and write to a card.
SD Host Controller (SDHC)
An SD host controller (SDHC) is a device capable of sending commands to an SD card. These commands can be sent using a system’s native SD card interface, or over SPI.
Applications should generally not use the SD host controller API directly, instead they should use Zephyr’s SD card subsystem.
Requests
The core of the SD host controller (SDHC) API is the sdhc_request() API.
Requests contain a sdhc_command command structure, and an optional
sdhc_data data structure. The caller may check the return code,
or the response field of the SD command structure to determine if the
SDHC request succeeded. The data structure allows the caller to specify a
number of blocks to transfer, and a buffer location to read or write them from.
Whether the provided buffer is used for sending or reading data depends on the
command opcode provided.
Host Controller I/O
The sdhc_set_io() API allows the user to change I/O settings of the SD
host controller, such as clock frequency, I/O voltage, and card power. Not all
controllers will support applying all I/O settings. For example, SPI mode
controllers typically cannot toggle power to the SD card.
Related configuration options: